Measuring and controlling of a flow are crucial contents for an integrated gas delivery system. One commonly used device is a mass flow controller (MFC), which controls the mass of the introduced gas or liquid tightly. Referring to the FIG. 1, a block diagram of a prior art MFC is shown. The prior art MFC comprises a sensor 11, an electromagnetic valve 12, a sensor driver circuit 14 coupled to the sensor 11 in order to receive a detection signal from that, an electromagnetic valve driver circuit 15 coupled to the electromagnetic valve 12 in order to adjust a flow through that, a microprocessor 13 coupled to the sensor driver circuit 14 and the electromagnetic valve driver circuit 15 respectively, and an A/D converter 16. Various parameters of the gas or the liquid introduced into a tubular shunt 17, such as a flow, a flow rate, etc., are sensed by the sensor 11 and converted into an electronic signal to be outputted to the sensor driver circuit 14 for processing. The A/D converter 16 converts an inputted setting signal into a first digital signal, and converts the processed signal outputted by the sensor driver circuit 14 into a second digital signal. The microprocessor 13 is coupled to the A/D converter 16 for receiving the first digital signal and the second digital signal to generate a flow control signal. Then, the electromagnetic valve driver circuit 15 converts the flow control signal outputted by the microprocessor 13 into an analog signal to control the electromagnetic valve 12, so as to control the flow and the flow rate of the gas or the liquid. Referring to the FIG. 2, which is a schematic diagram of a closed-loop circuit according to the prior art MFC. In general, the mechanism of the prior art MFC is a control system having a closed-loop circuit. A difference in a detection signal outputted by a sensor 21 and a setting signal is calculated by a PID module 22 and converted into a control voltage to control an openness of an electromagnetic valve 23, so as to control a flow of a fluid 24 tightly. Referring to the FIG. 3, a schematic diagram of an electromagnetic valve according to the prior art MFC is shown. The electromagnetic valve comprises an elastic component 31 positioned above a fluid inlet in order to generate an elastic force downward to close the fluid inlet, and an electromagnetic coil 32 around the elastic component 31 in order to generate an electromagnetic force opposite to the elastic force to open the fluid inlet when a current is provided. A balance between the elastic force and the electromagnetic force is required to adjust the height distancing the fluid inlet, so as to stable the flow rate of the fluid. However, the electromagnetic force is not proportionally related to the height. With the change of the height, nonlinear change of the electromagnetic force is obviously exposed out.
Although the conventional MFC may be adequate for a flow control at the point of 100% of a full scale, it has significant drawbacks of big overshoot and long response time for a flow control at the point of 2% of a full scale. It is difficult for a conventional MFC to ensure a timely control response for a flow rate at any point in a 2% to 100% of a full scale. Therefore, a new MFC is needed to precisely control a flow rate of the gas at any point in a 100% of a full scale, and also needed to meet the needs for various using environments.
Accordingly, it is an urgent problem to be solved that a new MFC is required to complete a precisely control for a flow rate in a wide scale.